Apparatus for diverting a stream of articles

ABSTRACT

Apparatus is disclosed for diverting a stream of articles, the apparatus including a framework, a first conveyor supported in the framework and conveying stream of articles along a first conveying surface, and a second conveyor supported in the framework parallel to the first conveyor and having a second conveying surface. A first drive mechanism drives the first conveyor at a first speed in a first direction, and a second drive mechanism drives the second conveyor at a second speed in a second direction opposite to the first direction. A carrier is arranged to travel along a path parallel to the first and second conveyors, and a diverter element is affixed to the carrier and extending across at least a portion of the conveying surfaces of the first and second conveyors to divert articles in the stream on the first conveyor to the second conveyor. A carrier drive mechanism is operatively configured to drive the carrier along the path at a speed and in a direction that depends on the first speed and the second speed. The carrier drive mechanism is disposed in a stationary position with reference to the framework. A controller calculates a differential speed corresponding to the difference in first and second speeds of the first and second conveyors respectively, and for controlling the carrier drive mechanism for driving the carrier at the differential speed.

RELATED APPLICATIONS

The present application is a Continuation Application of pending U.S.application Ser. No. 10/461,210, filed Jun. 13, 2003, which is aContinuation Application of U.S. application Ser. No. 10/317,952 filedDec. 12, 2002, and now granted as U.S. Pat. No. 6,585,104, which is aContinuation Application of U.S. application Ser. No. 09/803,564, filedMar. 9, 2001, and now granted as U.S. Pat. No. 6,497,321, all of whichare incorporated by reference herein, and to which benefit is claimedunder 35 U.S.C. § 120.

FIELD OF THE INVENTION

This invention relates generally to conveying systems having pluralpower-driven conveying sections and, more particularly, to apparatus forvarying the effective length of the system by controlling the diversionof conveyed articles from one conveyor section to another.

BACKGROUND OF THE INVENTION

Many conveyor applications require that articles transported on oneconveyor belt be transferred to another conveyor belt that may betraveling in another direction, such as the opposite direction.Stationary rails spanning the conveying surfaces of the belts at atransfer point are often used for this purpose. In some applications,such as article accumulation, the transfer point can be moved. Themoving transfer point allows the effective length of the conveying pathand, consequently, the amount of articles accumulated to be controlled.In a spiral accumulator, such as that shown in U.S. Pat. No. 6,152,291,two parallel conveyor belts—an infeed belt and outfeed belt—arehelically arranged with a rotatable transfer mechanism traveling betweenthem. The position of the transfer mechanism depends on the relativespeeds of the two oppositely-moving belts. A guide plate on the transfermechanism directs articles from the infeed conveyor belt to the outfeedbelt. A rotatable member in the transfer mechanism simultaneouslyengages drivers formed on the specially designed infeed and outfeedbelts. The rotatable member, driven by the drivers, translates thetransfer mechanism and its attached guide plate along the belts asdetermined by their relative speeds. The rotatable member rides alongwith the transfer mechanism.

A more common accumulation system is known as a bi-di (bi-directional)table. Typically, a bi-di table includes a bi-directional conveyor beltarranged to run perpendicular to a main conveyor belt. As articles buildup on the main conveyor belt, backpressure directs them onto the bi-dibelt, which runs in a direction away from the main conveyor. In thisway, articles are accumulated on the bi-di belt's surface. As downstreamprocesses require more articles, the direction of the bi-di belt isreversed so that the accumulated articles are pushed back onto the mainconveyor belt. These bi-di tables, which support the bi-di belt and itsdrive mechanisms, are generally rectangular in shape with drive or idlershafts for sprockets or pulleys at each end. But, unlike the spiralaccumulator, these simple, ubiquitous tables are not first-in, firstout.

Thus, there is a particular need for a simple first in, first-outaccumulation system, especially one that can be easily retrofitted in abi-di table. More generally, there is also a need for a simple mechanismfor diverting articles from one conveyor belt to another, such asoppositely-moving conveyor belts.

SUMMARY OF THE INVENTION

These needs and others are satisfied by a novel article-divertingapparatus embodying features of the invention. In the apparatus, a firstconveyor belt is driven in a first direction at a first speed. A secondconveyor belt is driven at a second speed in a different seconddirection, typically the opposite direction. A stream of articles isconveyed along a conveying surface of the first conveyor. A carriertravels along a path generally parallel to the first and second conveyorbelts. A diverter element affixed to the carrier extends across at leasta portion of the conveying surfaces of the first and second belts todivert articles in the stream from the first belt to the second belt.The carrier is controlled by a differential drive mechanism at a speedthat depends on the speeds of the first and second conveyor belts. Inthis way, the position of the diverter element and, hence, the transferpoint are determined by the relative speeds of the two belts.

In one version of the apparatus, the differential drive mechanism isstationarily attached to a framework supporting the carrier and thefirst and second belts. In another version, the differential drivemechanism is attached, not directly to the first and second belts, butto a first drive mechanism driving the first belt and to a second drivemechanism driving the second belt. This permits non-custom,less-expensive, standard belts to be used as the first and second belts.

In a first-in, first-out accumulator using the apparatus of theinvention, a stream of articles at an upstream position on a mainconveyor is supplied to the first, or infeed, conveyor belt, transferredto the second, or outfeed, conveyor belt by the diverter element on acarrier, and then fed by the second belt back to the main conveyor lineat a downstream location. The amount of accumulation is determined bythe carrier drive mechanism, which positions the carrier and diverterelement along the infeed and outfeed belts depending on their relativespeeds.

In other versions, the carrier is an endless carrier belt parallel tothe first and second belts. The belt can be an intermediate belt betweenand abutting the first and second belts with a transfer surface portionacross which products are transferred from the first belt to the secondbelt. Alternatively, the carrier belt flanks the first conveyor belt andcarries the affixed diverter element. The flanking belt can be used inconjunction with another flanking belt on the opposite side of thesecond conveyor that provides two-sided support for the diverterelement. In this version, the first and second conveyor belts can beabutted for direct transfer of articles from one to the other. In oneversion in which a carrier belt is used, the first and second beltsengage rotating elements including aligned shafts with sprockets aboutwhich the belts articulate. The differential drive mechanism isrotationally coupled to the rotating assemblies and engages the carrierbelt to drive at a speed that depends on the relative speeds of theconveyor belts. This version is especially easy to retrofit in anexisting bi-di table to achieve first-in, first-out capability.

In one version, the differential drive mechanism is differentiallygeared to the first and second drive mechanisms. But the belts andcarrier can alternatively be controlled by a controller thatindividually controls the drive mechanisms of the first and secondconveyor belts and the carrier. In either of these examples, the drivecharacteristics can be tailored for various applications by setting thespeed of the carrier to be as₁−bs₂, where s₁ is the speed of the firstconveyor belt, s₂ is the speed of the second conveyor belt, and a and bare adjustable parameters that are chosen to fit the application.

Thus, the apparatus provides clear advantages in diverting articles fromone conveyor belt to a parallel, oppositely moving conveyor belt.

According to certain other aspects of the invention, an apparatus isdisclosed for diverting a stream of articles, the apparatus including aframework, a first conveyor supported in the framework and conveyingstream of articles along a first conveying surface, and a secondconveyor supported in the framework parallel to the first conveyor andhaving a second conveying surface. A first drive mechanism drives thefirst conveyor at a first speed in a first direction, and a second drivemechanism drives the second conveyor at a second speed in a seconddirection opposite to the first direction. A carrier is arranged totravel along a path parallel to the first and second conveyors, and adiverter element is affixed to the carrier and extending across at leasta portion of the conveying surfaces of the first and second conveyors todivert articles in the stream on the first conveyor to the secondconveyor. A carrier drive mechanism is operatively configured to drivethe carrier along the path at a speed and in a direction that depends onthe first speed and the second speed. The carrier drive mechanism isdisposed in a stationary position with reference to the framework. Acontroller calculates a differential speed corresponding to thedifference in first and second speeds of the first and second conveyorsrespectively, and for controlling the carrier drive mechanism fordriving the carrier at the differential speed. Various options andmodifications are possible.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the inventions arefurther addressed in the following description, appended claims, andaccompanying drawings, in which:

FIG. 1 is an isometric view, partly cut away, of an apparatus embodyingfeatures of the invention, the apparatus including a diverter elementfor diverting a stream of articles;

FIG. 2 is a top plan view of the apparatus of FIG. 1;

FIG. 3 is an end elevation schematic of a stepped arrangement ofconveying surfaces usable in the apparatus of FIG. 1;

FIG. 4 is an isometric view of a drive mechanism, including adifferential drive, at one end of the apparatus of FIG. 1;

FIG. 5 is an isometric view of the opened-up differential drivemechanism of FIG. 4;

FIG. 6 is an isometric view of a drive mechanism at the opposite end ofFIG. 1 from the drive mechanism in FIG. 4;

FIG. 7 is a top plan view of another version of apparatus for divertingarticles, in which the diverter element is driven from one side;

FIG. 8 is a top plan view of another variation of diverter apparatus asin FIG. 7 with the diverter attached at flanking positions;

FIG. 9 is an isometric view of a portion of another version ofarticle-diverting apparatus partly cut away to show a differential drivefor a lead screw;

FIG. 10 is a side view of the lead screw drive of FIG. 9; and

FIG. 11 is a top plan schematic of a first-in, first-out accumulatorapplication using the apparatus of FIG. 1.

DETAILED DESCRIPTION

An apparatus embodying features of the invention for diverting articlesfrom a stream of articles is shown in FIGS. 1 and 2. The apparatusincludes a conveyor bed formed by a framework 20 with legs 21 and a pairof parallel upper support rails 22. Crossbeams 23 span the support railsat opposite ends 24, 25 of the conveyor bed. Cross supports 26 formingpart of the framework support a conveyor pan or wearstrips 27 thatunderlie the carryway of a first infeed conveyor 28 and a parallelsecond outfeed conveyor 30.

Each conveyor includes an endless belt, or chain, wrapped aroundrotating assemblies 32, 33 at the first and second ends 24, 25 of theconveyor bed. The belt, or chain, is preferably an endless modularplastic conveyor belt, such as any of those standard belts manufacturedand sold by Intralox, Inc. of Harahan, La., USA. Modular conveyor beltsare preferable because the modules can be easily linked together end toend and side by side with hinge pins typically in a bricklay pattern toconstruct belts of almost any length and width. But any belt, including,for example, metal chains or fabric belts, could be used effectively.The infeed belt 28 and the outfeed belt 30 are driven in the directionof arrows 34, 36.

In the example of FIGS. 1 and 2, the infeed belt 28 is driven by a firstinfeed drive mechanism 38, which is part of the second rotatingassemblies 33. The outfeed belt 30 is driven by a second outfeed drivemechanism 40, which is part of the first rotating assemblies 32. In thisdrive arrangement, the first and second drive mechanisms pull the beltsin tension along the conveyor carryway in the direction of the arrows34, 36. Motors 42, preferably variable-speed motors, in the infeed andoutfeed drive mechanisms rotate the rotating assemblies, which engagethe belts positively or frictionally, to drive the belts in thedirections shown.

The apparatus also includes a diverter element 44 that extends across atleast a portion of the width of the first and second conveyors. Thediverter element is attached to a carrier, in this example, anintermediate belt 46 disposed in the space 48 between the infeed andoutfeed belts. The intermediate belt is preferably a modular plasticconveyor belt, but could as well be a metal chain or a fabric belt. Onlya portion of the intermediate belt is shown in FIGS. 1 and 2 in order toshow other features of the apparatus, but the intermediate belt isco-extensive with the infeed and outfeed belts in that it is also anendless belt wrapped around the first and second rotating assemblies 32,33. The intermediate belt, positioned between the infeed and outfeedbelts, abuts each of them with only a minimal gap. (Siderails to confinearticles on the conveyor are not shown to simplify illustration.)

The diverter element 44 captures articles 50 from a stream of articleson the infeed belt 28 and directs them across a transfer surface 52 ofthe intermediate belt onto the outfeed belt 30 traveling in the oppositedirection. The diverter element has a guide surface 54, in this example,an arcuate surface, upstanding from a base 56. The base is attached to asection of the intermediate belt so that the diverter element moves withthe intermediate belt. Arms 60, 61 of the diverter element extend acrossat least a portion of the conveying surfaces of the infeed and outfeedbelts. In the version shown in FIGS. 1 and 2, the first arm 60 extendsacross most of the width of the infeed belt. In this case, all of thearticles 50 in the stream are received by the diverter element. But itis also possible to have a shorter first arm that would capture somearticles, but allow others to pass. The arms can ride directly on theinfeed and outfeed conveyors, or they can be positioned above theconveying surfaces as long as they are not so high as to allow articlesto be diverted to pass underneath in normal operation. A barrier 62 isalso attached to the intermediate belt. The guide surface of thediverter element and the barrier bound the transfer surface 52 of theintermediate belt. The barrier ensures that products are diverted onlyacross the transfer surface and not at other points along the carryway.For smooth transfer of product, the conveying surfaces of the infeed andoutfeed belts are preferably coplanar with the outer surface of theintermediate belt. It would also be possible, as shown in FIG. 3, tohave the conveying surfaces of the infeed 28 and outfeed 30 conveyorbelts and the outer surface of the intermediate belt 46 stepped down inelevation from the infeed belt to the outfeed belt. Alternatively, theentire conveyor bed could be slanted downward, off horizontal, towardthe outfeed belt to get an assist from gravity in clearing articles offthe transfer surface.

In the exemplary version of the apparatus shown in FIGS. 1 and 2, therotating assemblies 32 at the first end 24 of the conveyor bed are shownin more detail in FIG. 4. A first rotating assembly 64 and a secondrotating assembly 65 are coaxially arranged and terminate in adifferential drive mechanism 66. The first rotating assembly activelydrives the outfeed belt 30. The assembly is stationarily mounted to thecrossbeam 23. The assembly includes the drive motor 42, which, in thisexample, has a right-angle drive shaft 68. The first rotating assemblyincludes a shaft 69, which is shown segmented, on which sprockets 70 aremounted. Bearing blocks 72 support the shafts for rotation. The numbersof bearing blocks, sprockets, and shaft segments required depend on thewidth of the belt and its load. In this example, four sprockets, threebearing blocks, and two shaft segments are shown for the first rotatingassembly. The sprocket shaft 69 is connected to the motor drive shaft 68by a coupling 74. The other end of the sprocket shaft is connected to adifferential shaft 76 (FIG. 5) by a coupling 77. The sprockets haveperipheral teeth (shown in FIG. 4 as a raised portion to simplify thedrawing) that engage underside receiving structure in the outfeed belt,or chain, to drive and track it. In the case of a fabric belt, thetoothed sprockets are replaced by roller pulleys that frictionally drivethe belt.

While the first rotating assembly 64 at the first end of the belt formsa drive mechanism for the outfeed belt, the second rotating assembly 65is an idler assembly for the infeed belt 28. In this version of theapparatus, the drive mechanism for the infeed conveyor is in therotating assemblies 33 stationed at the other end 25 of the conveyorbed. Although this arrangement is preferable because both drivemechanisms are pulling the belts, the drives could be stationed at thesame end or, especially for long belts, distributed along the length ofthe belts. The idler assembly 65 is similar to the first rotatingassembly 64, but is not directly coupled to a motor. It is, however,coupled to the differential drive mechanism by a coupling 77. Thus, thedifferential drive mechanism is coupled to each rotating assembly, whichrotates at a speed corresponding to the speed of the associated belt.Each rotating assembly, whether including a drive shaft or an idlershaft, acts as an input drive mechanism to the differential drivemechanism.

The differential drive mechanism is shown in more detail in FIG. 5. Themechanism includes four bevel gears 78A-D. The differential shaft 76,rotating at the speed of the outfeed belt, is connected to the bevelgear 78A. The differential shaft 76′, rotating at the speed of theinfeed belt, is connected to the opposite bevel gear 78B. The gears meshwith gears 78C and 78D, which are coaxially and rotatably aligned aspinion gears on pinion shaft 80. Couplings 82 retain the bevel gears inplace on the shafts and pinion shaft. The ends of the pinion shaftextend from a spider 83, which also provides supports for thedifferential shafts 76, 76′. The differential mechanism fits in a hollow84 formed in the center of two mating central housing halves 86. Theends of the pinion shaft fit in cavities 88 formed radially in thehousing halves. Metal plates 89 serve as thrust bearings. Dowels 90register the two housing halves, which are held together conventionallyby bolts or screws through holes 92. A toothed sprocket wheel 94 isattached to each housing half. The peripheral teeth of the sprocketwheel engage the intermediate belt 46 to drive it.

The geared differential works conventionally in that relative motion ofthe shaft output bevel gears 78A and 78B causes the pinion gears 78C and78D to rotate about the axis of the differential shafts 76, 76′. As thepinion gears rotate, the ends of the pinion shaft 80 cause the housingand the sprocket wheels to rotate. The speed of rotation depends on therelative speeds of the rotation of the output shaft bevel gears. In thesituation where the outfeed belt and the infeed belt are moving at thesame speed in opposite directions, the outfeed output bevel gear 76rotates in one direction at a certain speed and the infeed output bevelgear 76′ rotates in the opposite direction at the same speed, whichcauses the pinion gear assembly to rest with its pinion shaftstationary. As one of the conveyor belts speeds up relative to theother, the differential drive mechanism causes the housing and sprocketwheel assembly to rotate in the direction of the faster moving rotatingassembly, but at half the difference between the speeds of each rotatingassembly. Thus, in this example, the speed s of the intermediate belt isgiven by s=½(s₁−s₂), where s₁ is the speed of the faster-moving belt ands₂ is the speed of the slower-moving belt. Of course, the gearing ratioscan be altered by the use of gear reducers or other conventionaltechniques to derive other speed relationships that may be genericallydefined by s is proportional to as₁−bs₂, where a and b are parametersset by the effective gear ratios, for example. This would allow theintermediate belt to be driven at a speed that is influenced relativelymore by one of the conveyor belts than the other in specialapplications.

The second rotating assemblies 33 stationed at the second end 25 of theconveyor bed are similar to those at the first with the followingdifference shown in FIG. 6. First, the drive motor 42 for the infeedbelt and its drive elements 96 are mounted on the crossbeam 23 at thisend. Second, idler elements 98 form the rotating assembly for the infeedbelt. Third, the rotating elements, although mounted coaxially, do notdrive a differential mechanism at this end. Instead, an idler sprocket100 on an idler shaft 102 supported by flanking bearing blocks 72 isprovided to support and track the endless intermediate belt 46 at thisend of the conveyor bed.

Another version of an apparatus for diverting articles is shown in FIG.7. In this version, the infeed belt 28 and the outfeed belt 30 abut eachother. The diverter element 44′ is carried by a carrier belt 104 nextto, in this example, the infeed belt. The diverter element extendsthrough a gap between stationary side rails 106 across the conveyingsurfaces of the infeed and outfeed conveyor belts to direct articlesfrom the first belt directly to the oppositely running second beltwithout having to traverse an intermediate belt—a distinct advantage.The carrier belt is driven differentially by the drive mechanisms ofeach of the conveyor belts. Because, in this version, the carrier beltis not adjacent to the outfeed belt, the drive mechanism of the outfeedbelt would have to be connected with the differential drive mechanism ofthe carrier belt through an intervening jackshaft or some otherconventional linkage.

A slightly modified alternative to the apparatus in FIG. 7 isillustrated in FIG. 8. In this version, a diverter element 44″ iscarried at each end by a carrier belt 104. This version provides bettersupport for the diverter element. The two flanking carrier belts areeach driven differentially in unison.

The versions described thus far are especially adaptable to beretrofitted into existing bi-di tables, which typically provide forsprockets, shafts, and motors at each end and include belt-supportingstructure along the carryway and returnway. Essentially, the bi-di beltand its drive and idler sprocket assemblies are replaced by the beltsand rotating assemblies of the invention. The remainder of the bi-diconveyor bed remains largely unchanged. As already mentioned, theversions described lend themselves to easy expansion through widening orlengthening of the belts.

To this point, the carrier for the diverter element has been describedas a belt (an intermediate belt or a carrier belt) differentially drivenby a differential drive mechanism connected to infeed and outfeed beltdrive mechanisms. In another version of the apparatus, shown in FIGS. 9and 10, the diverter element 44 is carried on a carrier 106, which isthe linearly variable nut of a lead screw 108. The lead screw isconnected at one end to a stationary differential gear 110 and at theother to a fixed bearing block 112 at the opposite end of the carrierrun. The speed and direction of rotation of the lead screw depend on therelative speeds of the infeed 28 and outfeed 30 belts. As the lead screwrotates, the carrier is driven linearly along its run. To minimize thespace between the two conveyor belts, the diverter element is connectedto the carrier by a thin, but sturdy, fin 114 that is attached to eachby welding, for instance.

All of these diverter carrier arrangements can be used to divertarticles from one conveyor to another and are useful, for example, in afirst-in, first-out article accumulator, such as the one shown in FIG.11. The accumulator system 116 effectively adjusts the length of aconveying path depending on the upstream supply of and the downstreamdemand for articles. A stream of articles 50 conveyed in the directionof arrow 118 by a main conveyor line 120 is received at an upstreamlocation 122 of the main conveyor by an infeed conveyor belt 28 drivenin the direction of arrow 34. An infeed guide rail 124 guides the streamof articles onto the infeed belt. As the infeed belt transports thearticles, they are captured and redirected by the diverter element 44attached to and carried by the intermediate belt 46. The articlestransfer across the transfer surface 52 of the intermediate belt betweenthe diverter element and the barrier 62 and onto the outfeed conveyorbelt 30. The diverted articles are delivered to the main conveyor at adownstream location 128 by the outfeed conveyor belt driven toward themain conveyor. An outfeed guide rail 125 guides the stream of articlesback onto the main conveyor. A transfer plate 126, such as a deadplate,is used for a smooth transfer of articles to and from the main conveyor.The main conveyor could alternatively use other transfer techniques,such as transfer belt edges attached to and moving with the mainconveyor belt. The infeed and outfeed belts need not be perpendicular tothe conveyor, but could, for example, run parallel to a main conveyorline that includes upstream and downstream segments on opposite sides ofthe infeed/outfeed belt unit. The accumulator allows the transport ofarticles along the main conveyor line to be adjusted for mismatchesbetween the upstream supply of and the downstream demand for articles.The accumulator does this by controlling the effective length of theconveying path. As the supply of articles increases, the infeed belt isdriven at a higher speed than the outfeed belt. The differentiallydriven carrier belt moves away from the main conveyor. With the diverterelement farther away from the main conveyor, more articles canaccumulate on the lengthened conveying path. As the demand for articlesdownstream increases to a level outstripping the supply of articles, theoutfeed conveyor is driven faster than the infeed conveyor. When thisoccurs, the carrier belt and its diverter element move toward the mainconveyor and shorten the effective conveying path and the proportionalaccumulation area. For protection, limit switches (not shown) at eachend of the infeed/outfeed conveyor bed cause the motors to stop when thediverter element gets to either end of its permissible range along theconveyor bed.

The supply of and demand for articles can be sensed by conventionalarticle sensors 130 positioned at, for example, upstream and downstreamlocations on the main conveyor. Their signals 132, 133 are electricallydirected to a controller 134, which further sends control signals 136,137 to the variable-speed drive motors 42 to adjust the speeds of theinfeed and outfeed belts. Although the differential drive mechanismsdescribed to this point are mechanically-coupled differentials, it wouldalternatively be possible to have an independent drive for the carrierwith the differential speed calculated by the controller and anappropriate speed control signal sent to the carrier's differentialdrive mechanism. With such an arrangement, the controller easily tailorsthe speed relationship (e.g., s=as₁−bs₂) to the needs of the system atany time. An operator adjusts the values of the a and b parametersthrough the controller.

Thus, the invention has been described with respect to various versionsby way of example. Even so, those skilled in the art will appreciatethat other versions are possible without materially departing from thenovel teachings and advantages of the invention. For example, thecarrier could ride on a rack and pinion arrangement, cable and drumarrangement, or a drag chain and rail arrangement. As another example,multiple intermediate drive mechanisms, including multipledifferentials, could be distributed along the conveyor, especially forlong belts. The belts could be radius, sideflexing belts arranged alonga curved path. The differential could be realized with spur gears orother gear types. As the examples suggest, these and other modificationsare intended to be included within the scope of the invention as definedin the following claims.

1. Apparatus for diverting a stream of articles, comprising a framework;a first conveyor supported in the framework and conveying stream ofarticles along a first conveying surface; a second conveyor supported inthe framework parallel to the first conveyor and having a secondconveying surface; a first drive mechanism for driving the firstconveyor at a first speed in a first direction; a second drive mechanismfor driving the second conveyor at a second speed in a second directionopposite to the first direction; a carrier arranged to travel along apath parallel to the first and second conveyors; a diverter elementaffixed to the carrier and extending across at least a portion of theconveying surfaces of the first and second conveyors to divert articlesin the stream on the first conveyor to the second conveyor; a carrierdrive mechanism operatively configured to drive the carrier along thepath at a speed and in a direction that depends on the first speed andthe second speed the carrier drive mechanism disposed in a stationaryposition with reference to the framework; and a controller forcalculating a differential speed corresponding to the difference infirst and second speeds of the first and second conveyors respectively,and for controlling the carrier drive mechanism for driving the carrierat the differential speed.
 2. The apparatus according to claim 1,wherein the carrier comprises a chain and rail arrangement.
 3. Theapparatus according to claim 1, further including article sensorspositioned at upstream and downstream locations on a main conveyor forsensing the supply of and demand for articles.
 4. The apparatusaccording to claim 1, wherein the controller receives electrical signalsfor controlling the carrier drive mechanism.
 5. The apparatus accordingto claim 1, wherein the carrier drive mechanism drives the carrier at aspeed proportional to as₁−bs₂, where s₁ is the speed of the firstconveyor, s₂ is the speed of the second conveyor, and a and b areadjustable parameters.
 6. The apparatus according to claim 1, whereinthe controller controls the first drive mechanism and the second drivemechanism.
 7. The apparatus according to claim 1, wherein the frameworkincludes a conveyor bed having legs and a pair of parallel upper supportrails.
 8. The apparatus according to claim 7, wherein crossbeams spanthe support rails at opposite ends of the conveyor bed.
 9. The apparatusaccording to claim 7, wherein each conveyor includes an endless loopmember wrapped around rotating assemblies at the first and second endsof the conveyor bed.
 10. The apparatus according to claim 9, wherein thedrive mechanism for the first conveyor is located in the rotatingassemblies stationed at the opposite end of the conveyor bed than thedrive mechanism for the second conveyor.
 11. The apparatus according toclaim 1, wherein framework includes cross supports that support aconveyor pan or wearstrips that underlie the first conveyor and thesecond conveyor.
 12. The apparatus according to claim 1, wherein thediverter element extends generally transverse to the first and secondconveying surfaces and has a length so as to extend from the carrier atleast partially across the first and second conveying surfaces to divertarticles from one of the first and second conveying surfaces to theother respective conveying surface.
 13. The apparatus according to claim1, wherein the diverter element includes a first arcuate arm extendingat least partway across the first conveying surface of the firstconveyor and a second arcuate arm extending at least partway across thesecond conveying surface of the second conveyor.
 14. The apparatusaccording to claim 1, wherein the first and second conveyors and thecarrier comprise belts.
 15. The apparatus according to claim 14, whereinthe carrier is arranged parallel to and between the first and secondconveyors.
 16. The apparatus according to claim 15, wherein theconveying surfaces of the first and second conveyors and the transfersurface of the carrier are coplanar.
 17. The apparatus according toclaim 1, wherein the first and second conveyors run perpendicular to amain conveyor that includes upstream and downstream segments on oppositesides of the first and second conveyors.
 18. The apparatus according toclaim 1, wherein an infeed guide rail guides the stream of articles ontothe first conveyor and an outfeed guide rail guides the stream ofarticles back onto the main conveyor.